Cobalt Metallacycles. 8. Preparative and Kinetic Studies on the Reactivity of Cobaltacyclopentadienes with Phosphites

Article abstract of DOI:10.1021/ja00533a013

(η⁵-Cyclopentadienyl)(triphenylphosphine)cobaltacyclopentadiene complexes, (CoCR¹=CR²CR³=CR⁴)(η⁵-C5H5)(PPh3) (1), react with phosphites, P(OR⁵)3 (2), yielding in successive steps (η⁵-cyclopentadienyl)(phosphite)cobaltacyclopentadiene complexes, (CoCR¹=CR²CR³=CR⁴)(η⁵-C5H5)5)3> (3) and isomeric 1-alkoxyphosphole oxide complexes (4).The structure of one isomer of the 1-methoxyphosphole oxide complex, 4ca-2, was determined by an X-ray crystallographic structural analysis.The complexes 4, when oxidized by Ce⁴⁺ ions, give 1-alkoxyphosphole oxides.Kinetic studies on the formation of 3 and the conversion of 3 to 4 have been carried out and a first-order reaction has been verified in the complex concentration for both steps.Activation parameters for the reaction of 1c (R¹, R², R³, R⁴ = Ph) with 2a (OR⁵ = OCH3) are determined as ΔH(excit.) = 31 kcal mol^-1 and ΔS(excit.) = 4 eu for the substitution, and as ΔH(excit.) = 22 kcal mol^-1 and ΔS(excit.) = -4 eu for the conversion step, respectively.The preparative and kinetic investigations show that (1) both steric and electronic factors of the substituents of the cobalt metallacycles govern the substitution step, and (2) the electronic factor chiefly governs the conversion step.The steric effect of the alkyl groups of 2 is very distinctive in the conversion step.